How do Atom Computer Ignition modules work?

[rvpapasso]

Since no one has answered how the Atom modules work I will give the non-technical explanation. With the traditional points and condenser system the points are mechanically opened when the current thru the magneto primary winding is at peak. This occurs when the flywheel magnets pass by the magneto laminations. At that unique time the points open which starts the energy transfer from the primary winding to the secondary winding to make a spark.

The Atom modules do the same with transistor circuitry. There are two circuits, one acts like points and the other is the trigger. The points circuit holds the coil primary to ground the same as the points do. The trigger circuit senses current thru the coil primary. When the trigger circuit senses peak primary current it tells the points circuit to release the primary from ground, the same as the points opening. When all the energy in the magneto is dissipated the circuits reset until the next cycle.

There are many advantages to using the Atom modules instead of points and condenser:

1) there are no contacts to pit
2) the spark is hotter since there are no energy losses due to a condenser and lack of a condenser also allows a faster decay of energy in the primary resulting in a higher secondary voltage
3) no moving parts so there is no wear
4) no adjustment required

There are some disadvantages:

1) timing can not be adjusted since the modules are not adjustable. For the average outboard you will not notice the difference and probably will notice an improvement in starting, idle and smoother top end. Given the wobble in the magneto plate on an old motor that causes excessive point bounce the modules will improve timing.

2) the modules create a spark based on the flywheel magnets passing by the magnetos. If the flywheel loses its timing in relationship to the crank there will still be a spark. This can damage an engine if the flywheel slips on the taper by creating a spark at the wrong time. Point systems do not have this problem since the point timing is directly from the crank.

I have been using the Atom modules for close to close to 20 years on my 1960 40hp Johnson and 18 years on my son’s 1967 33Hp Johnson with no failures or problems. Both engines run great and I noticed no degrade in performance when switching from points/condensers to the Atom modules. I also have used them on other OMC big twins and even a Cushman scooter with a 9Hp OMC OHV engine.

[legendre]

quote debe:

Hi lgendre, no the MJE13007A wont work because its not a Darlington type transistor so its gain (hfe) is too low. Ive tried a lot of transistors & failed until I found & tried 2SD1071. They are cheep I purchased 10 of them for $12.87 + $4.95 freight on Ebay from China. I suspect the Atom module used a custom made darlington transistor as it just had (atom A1) on it.

Oh, doh!

Right, right you are sir.. for some reason I was thinking the 13007 was a Darlington device. In fact, it’s a rather low-gain device that’s better suited to switching supplies and small-scale CRT horizontal output service. It’s a great general-purpose part for repairing the horiz. sweep circuits in numerous B&W / monochrome CRT displays, though.

I saw that ‘ATOM’ marking on the transistor.. not sure what to think. It’s a lot easier to have a batch of an off-the-shelf part run with your own markings, than to design & produce a proprietary transistor. Then again, who knows – we’d have to grab the ear of one of the Atom engineers!

FYI – for you geek types out there.. there are some pretty hard-core, high-voltage / current transistors to be salvaged from the "100W equivalent" CFL lamps. They use a part that’s very much along the lines of the mentioned MJE13007A – but I can’t attest to the topology (Darlington vs. conventional). You’ll also find a couple of high-voltage 105C caps inside those things as well.

[phil-b]

quote debe:

I found on some Ignition systems the transistor would break down. To over come this I added the 15KE200A to reduce the high voltage spikes. This then made the module reliable.

I wonder if adding external transient protection would make it possible to use a commercially available modules (that die quickly on outboards)?

[kennmatson]

Is that a diode in the pictures with the epoxy?

Kenn

[debe]

Ken the diode is a 15KE200A (1N6303A) Mosorb or Transient protector. Some of the Ignition coils have quite high voltage spikes that caused the module to shut down. Fitting it cured the problem.

[debe]

Phil B it will depend on the module & what it does, some are CDI. Ive tried the transient protector on a Nova module & it wont work on them.

[legendre]

I found an inexpensive source for the 2SD1071 transistors on eBay – item #181052048392

$4.95 + $2.00 ship for 10 pcs. So that’s 10 pcs. shipped for $6.95, or $0.69 per piece.

[frankr]

Senses the voltage reversal which occurs as the magnets pass by the coil legs???? Just my understanding, which may be completely off-base. And probably is.

[joecb]

A question for debe/ mumbles… in the last two pictures of the debe assembled unit there appears a component (cylindrical, black with silver band) the is not identified in the bill of materials or schematic. This component appears to be soldered across the two wire leads. What is this? looks like a diode or capacitor? Or am I not understanding something here.
And, thanks guys very good work on this issue, much appreciated.
Joe B

[ken-w]

quote debe:

Phil B it will depend on the module & what it does, some are CDI. Ive tried the transient protector on a Nova module & it wont work on them.

Debe, that’s a shame to hear about not being able to use a Transient protector to improve the reliability of the NOVAII modules. Did you only use the 200v that you used on your design? I has thinking about try a lower voltage to see if that helped.

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